(a) Field of the Invention
The present invention relates to an active-matrix-driven organic electroluminescence (EL) display device and, more particularly, to such an organic EL display device having a multilayer substrate.
(b) Description of Related Art
Recently, active-matrix-driven organic EL display devices are intensively developed. The active-matrix-driven organic EL display device has a plurality of unit pixels arranged in a two-dimensional array on a supporting substrate for utilizing the EL phenomenon in an organic thin film.
FIG. 1 shows an equivalent circuit diagram of a general active-matrix-driven organic EL display device (hereinafter referred to as simply organic EL display device) such as described in JP Patent Publication No. 8-234683. The organic EL display device includes a plurality of unit pixels 50 each having first and second TFTs 56 and 57 and a storage capacitor 58, a plurality of data lines 54 each disposed for the unit pixels 50 arranged in a column direction (Y-direction) and a plurality of scan lines 53 each disposed for the unit pixels 50 arranged in a row direction (X-direction). Each scan line 53 is supplied with scan signals by a scan driver (Y-driver) 51 and connected to gates of the first TFTs 56 in the unit pixels 50. Each data line 54 is supplied with data signals by a data driver (X-driver) 52 and connected to the drain of the first TFT 56 in each of the unit pixels 50. The source of the first TFT 56 is connected to the gate of the second TFT 57 and a first terminal of the storage capacitor 58 which has a second terminal connected to the ground. The drain of the second TFT 57 is connected to a cathode of an organic EL element or pixel EL element 41, the anode of which is connected to a common source line.
FIG. 2 shows a cross section of the unit pixel 50 in a conventional organic EL display device such as shown in FIG. 1. The unit pixel 50 includes a glass substrate 64, and a p-type active Si (p-Si) film 61 implementing source/drain regions, a gate insulator film 62, and a gate electrode 65, which are consecutively formed on the glass substrate 64 to configure the second TFT. Source and drain electrodes 63 are formed on the gate insulator film 62 and connected to the active p-Si film 61 through via holes. The unit pixel 50 also includes a planarization (insulator) film 66 covering the TFTs, and an organic EL element or pixel EL element including an anode 68 made of ITO, an organic thin film 91 and a cathode 92, which are consecutively formed on the planarization film 66. The anode 68 is connected to the source of the second TFT. It is to be noted that the first TFT, the storage capacitor and other interconnects (not depicted) are also formed overlying the glass substrate 64.
FIG. 3 shows another conventional organic EL display device in cross section, and FIG. 4 shows a schematic perspective view thereof. This type of organic EL display device is described in a JP Utility Model Publication No. 4-31299. In the organic EL display device, an EL panel 110 mounting thereon organic EL elements and a TFT panel 120 mounting thereon TFTs, storage capacitors and interconnects are bonded together, with the electrodes of the EL panel 110 and the corresponding electrodes of the TFT panel 120 being connected by metallic bumps 136
The EL panel 110 includes an EL substrate 111, and a transparent anode 112, a first insulator film 113, a ZnS luminescent film 114, a second insulator film 115 and a metallic cathode 116, which are consecutively formed on the EL substrate 111. The TFT panel 120 includes an EL substrate 121, and a gate electrode 122, a gate insulator film 123, an amorphous Si (a-Si) film 124 and a channel protective film 125, which are consecutively formed on the TFT substrate 111. Source electrode 130 and drain electrode 131 are also formed on the TFT substrate 121. In FIG. 4, the TFT panel 120 mounts thereon the EL panel 110. The can terminals 132 for the scan lines 53 are disposed at both the sides of the TFT panel 121, whereas data terminals 133 for the data lines 54 are disposed at both the top and bottom of the TFT panel 121. Ground terminals 134 and anode terminals 135 for the transparent electrode (anode) are disposed at the corner areas of the TFT panel 121.
In the conventional organic EL display devices, the screen size of the display device substantially defines the size of the glass substrate 111. Thus, a larger-screen display panel necessitates employment of a larger glass substrate, on which TFTs are fabricated. A larger glass substrate requires a larger fabrication facility including deposition and exposure systems and raises the fabrication costs for the organic EL display device. In addition, the large, number of unit pixels, formed on the large glass substrate etc., suffer from a lower ratio of the number of non-defective products to the number of total products due to the irregularities on the large glass substrate in the fabrication process.
It is therefore an object of the present invention to provide an active-matrix-driven organic EL display device which is capable of reducing the dimensions of the substrate on which TFTs are fabricated as well as reducing the fabrication costs therefor by raising the ratio of the number of non-defective products to the number of total products.
The present invention provides an active-matrix-driven organic electroluminescence (EL) display device including first and second substrates, a plurality of unit pixels each including a pixel EL element and a pixel circuit, the pixel EL elements being arranged in a matrix on a front surface of the first substrate, a plurality of scan lines each disposed for a corresponding row of the unit pixels, a plurality of data lines each disposed for a corresponding column of the unit pixels, a drive circuit for driving the scan lines and the data lines to activate the pixel EL elements through respective the pixel circuits, the second substrate mounting thereon the drive circuit, the scan lines, the data lines and the pixel circuits, the first substrate mounting thereon the second substrate at a rear surface of the first substrate.
In accordance with the organic EL display device of the present invention, since the pixel circuit for driving a corresponding pixel EL element of a unit pixel is disposed outside the pixel area, the dimensions of the substrate mounting thereon the pixel circuit can be reduced compared to the dimensions of the substrate in the conventional organic EL display device, the MOSFETs in the pixel circuit can be fabricated at lower costs and with higher ratio of the number of non-defected products to the number of total products.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.